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United States Department of Agriculture

Agricultural Research Service

Title: Evidence for Preferential Movement of Groundwater in Wetland Systems

Authors
item Angier, Jonathan
item McCarty, Gregory

Submitted to: American Society of Agronomy Meetings
Publication Type: Abstract Only
Publication Acceptance Date: October 27, 1999
Publication Date: N/A

Technical Abstract: The capacity for wetland systems to remediate contaminated groundwater is largely dependent on contact between the groundwater and the soils. However, preferential flowpaths may dominate the movement of groundwater through these soils. The study site, a small first-order stream with a riparian buffer strip adjacent to an agricultural field, contains an area where high-nutrient groundwater is reaching the stream. Physical evidence of preferential groundwater flow includes macropores and layers of high hydraulic conductivity. Conductivity of soil layers within this riparian wetland ranges from 10-4 to 10-7 m3/s. High conductivity layers typically consist of semicontinuous bands of sand and/or extremely soft, low-density material within denser, finer-grained soils. Transects of nested piezometers allow for sampling of groundwater, hydraulic conductivity measurements, and determination of hydraulic gradients. Preferential flowpaths and high vertical hydraulic gradients enable the contaminated groundwater to surface as upwelling zones, where secondary channels carry the water quickly to the stream. Discharge measurements combined with nitrate concentration data indicate that one dominant secondary channel system alone accounts for approximately 65% of the total increase in groundwater nutrient flux along this portion of the stream.

Last Modified: 9/10/2014
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